What does it mean for a husband and wife to be "spiritually one" in God's eyes?
This is speaking of the union of all born-again people in Christ and the leveling and homogenizing effect of this union. Christ is the uniting and equalizing constant among all those who know and love him. This isn't quite the same thing as the "one flesh" circumstance of a husband and wife, though, right?
It's not an unreasonable assumption, but their hiding being a reflection of their shame at their nakedness isn't clearly indicated in the account, or in any commentary on the event in other parts of Scripture. What the account does point out as a motive for Adam's hiding was fear, not shame. Why do you suppose the account highlights Adam's fear rather than shame?
Well, again, this is answering "why?" with a what. What Adam and Eve did was allow themselves to be tempted by the serpent, choosing to disobey the explicit, direct command of their Creator. But describing this doesn't explain why they did these things. Were Adam and Eve entirely incapable of resisting the temptation of the serpent? Was it inevitable that Adam and Eve would yield to its invitation to sin? If so, how do we know this and are they then responsible for partaking of the Forbidden Fruit? If Adam and Eve could have resisted the seduction of the serpent, why didn't they? Does the account of the Fall in Genesis give any explanation as to why the serpent's temptation was so effective? Adam and Eve weren't gullible children, nor were they at all deprived of food or comfort. Just the opposite, in fact. What's more, they met with God in the Garden. Why, then, did they succumb to the serpent's temptation? It seems to me that they should have been able to dismiss the serpent's temptation with ease.
But, again, this isn't indicated in the account at all. And nowhere else in Scripture (that I'm aware of, anyway) is it said that God clothing Adam and Eve in the skins of animals was a sacrifice for their sin. This is entirely an assumption you're making here and so you should be very careful about asserting it as hard fact.
Well, is this what the Bible indicates? Does it locate all sin in the devil? Or is the inclination to sin inherent in human nature, like scales are to fish, or wings are to birds? See James 1:14-16 and Romans 8:5-8. It seems to me that the devil simply provokes what is already present in human beings.
A husband and wife who are Spiritually born again and indwelled with the Holy Spirit means they, like all of us are one in the Lord. We are all one body in Christ with He being the Spiritual head of the body, Colossians 1:18. The man is to be the Spiritual head of his family, Ephesians 5:23.
Gal 3:26 For ye are all the children of God by faith in Christ Jesus.
Gal 3:27 For as many of you as have been baptized into Christ have put on Christ.
Gal 3:28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.
Gal 3:29 And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise.
1Corinthians 6:17 But he that is joined unto the Lord is one spirit.
God did not make woman to walk behind the man or to be less equal to him, but was created as a helpmate to walk beside him. It's like how both complete each other.
I can't say for a fact that they were ashamed of being naked, but they did sew fig leaves together to cover their nakedness (shame), not because they were in fear of God seeing them as that happened before God called out to them. I would say we were all once ashamed of nakedness (sin) before the Lord as that is why we humbled ourselves before Him with a heart of repentance.
I already explained why they allowed themselves to be tempted as it was the lust of the eye that caused them to disobey God's command. I don't know any other way to explain that as they made their first freewill choice. Anyone is capable to resist temptations, but as we can see beginning with Adam and Eve we have all fallen short at times. We don't know the mind of others and why they would allow themselves to fall short. None of us can answer for why Adam and Eve feel to the temptation, especially when God had placed them in the garden and provided everything for them.
Let me ask you this question, why do you fall to the temptation to sin at times as we all do?
Since we are made in the image of God then none of us were born sinful for God's image has no sin nor did we come out of the womb with sin upon us. Sin is a personal choice of a person rather than something passed on from generation to generation as we are not held accountable for the sins of our fathers, but it is our responsibility to not repeat those sins, Ezekiel 18:20.
Satan is an occasional and indirect cause of all our sins insofar as this created spirit (fallen angel) induced the first man to sin insofar as because of Adam's sin, human nature has been impaired to such an extent that we are all inclined towards sinning. Satan does not cause anyone to sin as that is by our own choices we make.
It was Adam and Eve's choice to disobey God by allowing themselves to be deceived by Satan working through that serpent who comes to kill, steal and destroy those who are God's own, John 10:10; 1Peter 5:8